Studies will be conducted to investigate the physicological function of enkephalins as well as their interaction with prostaglandins (PGs). Such studies will involve specific sites in the CNS and periphery where the enkephalins are known to act, namely the rat periaqueductal gray (PAG) and guinea pig ileum respectively. In particular, we will continue to investigate our recent finding that PGE1 and E2 are highly potent in reversing enkephalin block of electrically induced contractions of guinea pig longitudinal muscle-myenteric plexus preparation. The question of whether such antagonism occurs in the CNS will be examined by applying enkephalins and PGs directly to the PAG using microcannulas. In addition, we will determine whether such interaction can be demonstrated by binding studies involving subcellular fractions of PAG and ileum. Enkephalin uptake and release in guinea pig longitudinal muscle-myenteric plexus will be studied using radioactively labeled peptides. Inhibitors of peptidases which hydrolyze enkephalins will be stuided; these include D-phenylalanine, hydrocinnamic acid, leucyl valine, and bacitracin. We will determine whether such peptidase inhibitors potentiate exogenous enkephalin action, potentiate electroanalgesia of the CNS, increase endogenous enkephalin levels, and increase amounts of enkephalins isolated when the ileum and brain are stimulated tetanically. Whether such compounds produce analgesia will also be ascertained. We will investigate the possibility that prostaglandin synthetase inhibitors (e.g., indomethacin) can delay the development of tolerance to the analgesic effect of enkephalins. Such studies are based on the possibility that enkephalins, just as the opiates, may induce PG synthetase, the resulting increase of PG levels counteracting the action of the enkephalins and thus giving rise to tolerance.